Browsing by Author "Karsu Asal E.C."
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Item Luminescent properties of scintillator nanophosphors produced by flame spray pyrolysis(Elsevier B.V., 2017) Yildirim S.; Karsu Asal E.C.; Ertekin K.; Celik E.In the present work flame spray pyrolysis synthesis and characterization of the nano-scale phosphors; M′-YTaO4 and M′-Y(Ta0.85Nb0.15)O4 have been studied for the first time. Phase and elemental analysis of the produced nanophosphors were carried out by X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) measurements, respectively. The surface morphology and particle size of the nanophosphors were identified using scanning electron microscopy (SEM). The XRD results reveal that the nanophosphors have monoclinic M′-YTaO4 and M′-Y(Ta0.85Nb0.15)O4 phases belonging to the presence of M´-form of fergusonite structure. The particle sizes of the nanophosphors were found to be in the range of 50–100 nm. The spectroscopic characterization was performed by both radioluminescence (RL) and thermally stimulated luminescence (TSL) measurements after exposure to X-ray irradiation. Also, photoluminescence and decay times were investigated under UV excitation. The nanophosphors can be concluded as appropriate emissive materials for imaging, display and scintillator applications due to the efficient photoluminescence, moderate radioluminescence (RL) and thermally stimulated luminescence characteristics. © 2017 Elsevier B.V.Item Thermoluminescence response of CaF2:Dy as a function of irradiation temperature between room temperature and 270 °C(Elsevier Ltd, 2018) Karsu Asal E.C.; Polymeris G.S.; Kitis G.The Themoluminescence (TL) response of CaF2:Dy (TLD-200) as a function of irradiation temperature was studied in the present work. The irradiation of a TL material at elevated temperatures has a twofold scope: (a) To provide knowledge and insight regarding the possibilities of radiation dosimetry at high temperature environments; (b) The fact that during irradiation at elevated temperatures trap filling and trap emptying take place simultaneously, makes this pre-conditioning the most promising for the reflection in the net glow-curve of competition effects between traps and centres. The irradiation temperature (Tirr) region was between room temperature (RT) and 270 °C in steps of 10 °C. Using the same conditions as far as dose and temperature are concerned, post irradiation annealing (PIA) measurements were also performed, which give only the results of trap emptying. Both experiments were performed using (a) one sample for all measurements (single-aliquot procedure) and (b) two samples for each temperature (multi-aliquot procedure). Deconvolution was also applied in all cases towards investigating the impact of the two protocols on the kinetic parameters of all peaks for this specific material. The results showed that there is not any dependence of the TL response in the case of multi-aliquot procedure. However, in the case of single-aliquot procedure, a very interesting dependence of the TL response on Tirr is observed only for the last TL peak of TLD-200. These results, although weaker, were also observed in the case of PIA procedure. Activation energies of the high-temperature, more stable peaks yield a dependence on both irradiation and PIA temperatures. The results are discussed in the framework of the trap competition models. © 2018Item Thermoluminescence glow-curve deconvolution using analytical expressions: A unified presentation(Elsevier Ltd, 2021) Peng J.; Kitis G.; Sadek A.M.; Karsu Asal E.C.; Li Z.This study provides a unified presentation of thermoluminescence (TL) glow-curve deconvolution within the framework of the open source R package “tgcd”, according to various analytical expressions that describe first-, second-, general-, and mixed-order kinetics as well as the recently developed semi-analytical expressions that derive from the one trap-one recombination center (OTOR) model that utilizes the Lambert W function or the Wright Omega function. We provide a comprehensive, flexible, convenient, and openly accessible program to analyze TL glow curves according to different models and expressions. The consistency of kinetic parameters determined using different model expressions was assessed using measured TL glow curve of CaF2:Dy. The performance of the computerized glow curve deconvolution (CGCD) method was also tested using simulated glow curves. Results revealed the benefits of comparing kinetic parameters determined from different model expressions and those obtained using experimental TL evaluation methods to assess the reliability of deconvolution results. The accuracy of the CGCD method is dependent upon both the model expressions used and the intrinsic trapping parameters of the TL material. © 2020 Elsevier LtdItem Luminescent properties of natural amazonite from Pakistan(Springer Science and Business Media B.V., 2023) Karsu Asal E.C.Since anomalous fading (AF) is a problem for ThermoLuminescence (TL) dating (Sfampa et al. in Nucl Instrum Methods Phys Res Sect B Beam Interact Mater Atoms 320:57–63, 2014), the current work examines both AF and Isothermal Decay (ID) of TL signals of amazonite from Tangir Valley, Gilgit-Pakistan. It is supposed that any previous research has not been done on either the AF of this amazonite or the ID characteristics. Apart from the general-order kinetic theory, the obtained signals do not highly dependent on temperature. This can be taken as a kind of direct experimental proof that the amazonite may exhibit tunnelling processes (Sfampa et al. in Nucl Instrum Methods Phys Res Sect B Beam Interact Mater Atoms 320:57–63, 2014). The ID curves were investigated and discussed in the context of the tunnelling kinetic model of TL. © 2023, Akadémiai Kiadó, Budapest, Hungary.Item Low temperature luminescence and tunnelling effect in the Sr4Al14O25 co-doped with Eu2+and Dy3+ persistent luminescent phosphor(Elsevier Ltd, 2023) Karsu Asal E.C.Thermoluminescence (TL) technique is very useful in the research of persistent Luminescence (PL) phosphors. It gives information about the existence of energy levels within the forbidden band and lifetime. The TL glow curve of Sr4Al14O25: Eu2+,Dy3+ persistent phosphor consists of two well-separated glow peaks at around 353 K and 438 K after both UV radiation and beta irradiation. To study the low temperature (≤ room temperature) glow peaks, low temperature TL (LTTL) measurements were performed with a homemade system after exposed to UV radiation. The sample was heated according to T(t)=T∞−(T∞−T0)e−αt equation starting from liquid nitrogen temperature, 77K. Besides the peaks at around 345 and 445 K according to LTTL results, Sr4Al14O25: Eu2+,Dy3+ has two more well-separated low temperature TL peaks at around 170 K and 295 K. The lifetime of the TL glow peaks (at 353 K and 438 K) was calculated according to [Formula presented] and the results were checked with fading tests. Moreover, TL sensitivity tests were carried out both with and without preheating. Finally, tunnelling effect was evaluated by using the results of sensitivity tests and fading tests. Interesting results were observed at sensitivity tests performed with preheating. The results indicates that the behaviour of two glow peaks is very different from each other. The mechanism behind the peak around 438 K is localised transition involving a tunnelling effect. © 2022 Elsevier Ltd